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brianok
2001-Dec-03, 08:08 PM
I've never heard of this mission which is set for 2002, sounds quite fascinating.


http://einstein.stanford.edu/index.html

GrapesOfWrath
2001-Dec-04, 07:08 AM
It's been "imminent" for decades.

I find the concept of the navigation fascinating--they want to study a rotating sphere in a path around the Earth unhindered by friction, so they encase the sphere in another satellite and actively monitor the spheres position to keep it centered. The outside satellite runs interference for the sphere.

GrapesOfWrath
2001-Dec-15, 02:37 PM
NASA launch forecast (http://www-pao.ksc.nasa.gov/kscpao/schedule/mixfleet.htm) shows it October of 2002, from Vandenberg. Hmmm, just enough time to come up with a new theory of gravity...

NubiWan
2004-Apr-19, 01:26 PM
What happened to Probe A, and when did they know...?
:wink:
The big day is finally here, now we will learn what we pretty much allready know, but still...

http://www.ksc.nasa.gov/elvnew/gpb/index.htm

http://www.gravityprobeb.com/

ToSeek
2004-Apr-19, 01:34 PM
What happened to Probe A, and when did they know...?


Gravity Probe B FAQ: What happened to Gravity Probe "A"? (http://einstein.stanford.edu/content/faqs/faqs.html#GPA)

GP-A was a suborbital mission launched in 1976.

Extravoice
2004-Apr-19, 03:19 PM
While we're on the topic, I read in in the FAQ (http://einstein.stanford.edu/content/faqs/faqs.html) that the launch window for "Gravity Probe B" is extrememly short. Any ideas why?

If the thing is going into orbit (and not going to rendezvous with another object ) it seems that launch time would be pretty-much irrelevent. What am I missing?

ToSeek
2004-Apr-19, 03:27 PM
While we're on the topic, I read in in the FAQ (http://einstein.stanford.edu/content/faqs/faqs.html) that the launch window for "Gravity Probe B" is extrememly short. Any ideas why?

If the thing is going into orbit (and not going to rendezvous with another object ) it seems that launch time would be pretty-much irrelevent. What am I missing?

That they're using a preselected guide star (http://einstein.stanford.edu/content/faqs/faqs.html#guidestar) that needs to be continuously visible?

ToSeek
2004-Apr-19, 05:04 PM
Launch has been postponed at least until tomorrow (12:57:24 pm EDT). Upper level wind conditions changed, and there wasn't enough time to update the profile on the launch vehicle and verify that the update was correct.

Extravoice
2004-Apr-19, 06:20 PM
they're using a preselected guide star (http://einstein.stanford.edu/content/faqs/faqs.html#guidestar) that needs to be continuously visible?

Makes sense to me. I should have read a little further into the FAQ. :oops:

Thanks.

NubiWan
2004-Apr-20, 03:05 PM
Absolutely, there is simply nothing to the "Transdimentional Rift" rumor at all, that Probe A had fell into.... Think yesterday's launch window was only 60 seconds, welp, better luck today. :)

Kaptain K
2004-Apr-20, 04:27 PM
From what I've read, Gravity Probe B has a one second launch window! :o

The Bad Astronomer
2004-Apr-20, 04:33 PM
GP-B is ready for launch. As I write this, it's go for launch in 20 minutes! Watch it on NASA TV (http://www.nasa.gov/ntv).

R.A.F.
2004-Apr-20, 05:12 PM
Looks like smooth launch...thanks, BA, for that "heads up'. If you hadn't posted that I would have missed the whole thing!

Normandy6644
2004-Apr-20, 05:12 PM
GP-B is ready for launch. As I write this, it's go for launch in 20 minutes! Watch it on NASA TV (http://www.nasa.gov/ntv).

Successful launch! My timing was perfect, as I saw your post about a minute before it started.

scottmsg
2004-Apr-20, 05:16 PM
I missed the launch by 9 minutes. #-o . That will teach me for eating lunch when I should've been reading the board.

Normandy6644
2004-Apr-20, 05:25 PM
I missed the launch by 9 minutes. #-o . That will teach me for eating lunch when I should've been reading the board.

Exactly! See, you're learning well. NEVER leave the board. :lol:

R.A.F.
2004-Apr-20, 05:35 PM
NEVER leave the board. :lol:

We can leave the board??? :)
I wasn't aware of that option. :lol:

lpetrich
2004-Apr-22, 08:43 PM
I also watched the launch; however, I have not been able to find out anything since the separation of GP-B from its booster rocket's second stage.

ToSeek
2004-Apr-23, 10:58 PM
Gravity Probe B is Working fine (http://www.universetoday.com/am/publish/gravity_probe_b_working_fine.html?2342004)

George
2004-Apr-24, 08:46 PM
=D> =D> =D>

ToSeek
2004-Apr-27, 04:38 PM
A Pocket of Near-Perfection (http://science.nasa.gov/headlines/y2004/26apr_gpbtech.htm) - good Science@NASA article about the purpose and implementation of Gravity Probe B.

ToSeek
2004-Apr-30, 09:14 PM
All Systems Go On Gravity Probe B (http://www.sciencedaily.com/releases/2004/04/040430053259.htm)


In its first week on orbit, Gravity Probe B has achieved many successes that will ensure a smooth transition into the science phase of the mission and the best possible experimental accuracy. The spacecraft has already achieved a science mission orbit, within the plane of the Guide Star, IM Pegasi, and its inclination error is six times better than expected.

ToSeek
2004-May-26, 04:22 PM
Gravity Probe B Reaches One-month Milestone (http://www.sciencedaily.com/releases/2004/05/040525062554.htm)


One month into the mission, all spacecraft subsystems are continuing to perform well. The spacecraft's orbit remains stable and meets our requirements for next month's transition into the science phase of the mission, upon completion of the spacecraft initialization and orbit checkout. The four gyroscopes are suspended, and we have indications that they are rotating slightly in their housings.

ToSeek
2004-Jun-22, 01:43 AM
Update on Gravity Probe B (http://www.universetoday.com/am/publish/update_gravity_probe_b.html?1962004)


Designed to test two of Einstein's predictions about the nature of gravity and relativity, NASA's Gravity Probe B spacecraft is about halfway through the initialization and checkout phase of its mission. Mission operators have transmitted more than 5,000 commands to the spacecraft, and everything seems to be functioning properly, including its gyroscopes and the targeting system that keeps it locked onto the guide star: IM Pegasi. If everything continues to go as planned, it should begin scientific operations in August, and deliver the final results in a year.

Normandy6644
2004-Jun-22, 04:18 AM
Update on Gravity Probe B (http://www.universetoday.com/am/publish/update_gravity_probe_b.html?1962004)


Designed to test two of Einstein's predictions about the nature of gravity and relativity, NASA's Gravity Probe B spacecraft is about halfway through the initialization and checkout phase of its mission. Mission operators have transmitted more than 5,000 commands to the spacecraft, and everything seems to be functioning properly, including its gyroscopes and the targeting system that keeps it locked onto the guide star: IM Pegasi. If everything continues to go as planned, it should begin scientific operations in August, and deliver the final results in a year.


Awesome. Looking forward to the data. Thanks ToSeek!

Chip
2004-Jul-19, 05:04 AM
They even have a free, full color, downloadable scale paper model ...
DARN!

The requested URL /p_model/gpb_hq_pmodel.pdf was not found on this server.

Its a PDF file found near the bottom of their homepage (http://einstein.stanford.edu). Also, their "Relativity Q&A" page is very interesting. Its found under "gp-b classroom" on the homepage, and the answers are from Dr. Sten Odenwald.

Squink
2004-Jul-19, 11:54 PM
They even have a free, full color, downloadable scale paper model of Gravity Probe B that you can cut out and assemble!

DARN!

The requested URL /p_model/gpb_hq_pmodel.pdf was not found on this server.

Trinity
2004-Jul-20, 12:40 AM
I recall reading that, though I thought it had already happened...I must be on crack.

Chip
2004-Jul-20, 01:37 AM
They even have a free, full color, downloadable scale paper model ...
DARN!

The requested URL /p_model/gpb_hq_pmodel.pdf was not found on this server.

Its a PDF file found near the bottom of their homepage (http://einstein.stanford.edu). Also, their "Relativity Q&A" page is very interesting. Its found under "gp-b classroom" on the homepage, and the answers are from Dr. Sten Odenwald.

ToSeek
2004-Jul-20, 09:12 PM
Predecessor thread to this one (http://www.badastronomy.com/phpBB/viewtopic.php?t=12947) (with the same title and everything! ;) ) Numerous links on there - not sure how many of interest.

Chip
2004-Jul-20, 09:44 PM
Predecessor thread to this one (http://www.badastronomy.com/phpBB/viewtopic.php?t=12947) (with the same title and everything! ;) ) Numerous links on there - not sure how many of interest.

Cool.
BTW - before I posted this one, I figured someone must have posted about GPB and I was going to contribute, so I used the search feature and found nothing. 8-[

ToSeek
2004-Jul-20, 09:47 PM
Predecessor thread to this one (http://www.badastronomy.com/phpBB/viewtopic.php?t=12947) (with the same title and everything! ;) ) Numerous links on there - not sure how many of interest.

Cool.
BTW - before I posted this one, I figured someone must have posted about GPB and I was going to contribute, so I used the search feature and found nothing. 8-[

For some reason if you search on "Gravity Probe B" nothing turns up, but if you do just "Gravity Probe" it does. Don't ask me why. (Meanwhile, I had the advantage of knowing that there was a previous thread.)

Chip
2004-Jul-20, 11:07 PM
...(Meanwhile, I had the advantage of knowing that there was a previous thread.)

That's why you're a "PostDoc!" :D

milli360
2004-Jul-21, 05:38 AM
ToSeek:
For some reason if you search on "Gravity Probe B" nothing turns up, but if you do just "Gravity Probe" it does. Don't ask me why. (Meanwhile, I had the advantage of knowing that there was a previous thread.)
As near as I can tell, searching for words of four letters and shorter return null sets. Had you searched for "gravity probe b" and did not use the "Search for all terms" option, you would have had 10046 posts returned. More, now.

ToSeek
2004-Sep-09, 04:08 PM
Official press release:

NASA Gravity Probe B mission enters science phase, ready to test Einstein's theory (http://www.spaceref.com/news/viewpr.html?pid=14989)


Gravity Probe B (GP-B), a NASA spacecraft to test two predictions of Albert Einstein's general theory of relativity, achieved a major milestone this past week with the completion of the Initialization and Orbit Calibration (IOC) phase of its mission and the transition into the science phase. The GP-B mission is now one step closer to shedding new light on the fundamental properties of our universe

ToSeek
2004-Sep-13, 04:07 PM
And now it's obsolete?

Neutron stars steal space probe's glory (http://www.newscientist.com/news/news.jsp?id=ns99996372)


It has taken almost 50 years to conceive and build and has cost more than $700 million, but now NASA's Gravity Probe B spacecraft could be upstaged by telescopes on the ground.
...
Meanwhile, astronomers have been studying binary pulsars - two rapidly spinning neutron stars orbiting each other - to measure these effects. The gravitational fields of pulsars are so strong that both of the forces predicted by Einstein should show up relatively clearly in the precession of each pulsar in a binary system, much like that in a gyroscope.

scourge
2004-Sep-14, 02:02 AM
That's awesome - go astronomers! ;)

I'm itching to see how close the frame-dragging calculations of GR correspond to the data...Gravity probe's data will be within 1% experimental accuracy...ooooh. But the binary pulsar data may require significant assumptions regarding their moments of inertia, which sounds imprecise.

Sadly, they're both two to three Years away from conclusions on the frame-dragging aspect :(

milli360
2004-Sep-14, 02:14 AM
Some researchers have already announced results using the LAGEOS orbitting rocks.

scourge
2004-Sep-14, 02:36 AM
Some researchers have already announced results using the LAGEOS orbitting rocks.

Well great, how close do they conform to expectations milli360?

milli360
2004-Sep-14, 09:41 AM
Princz had some info on it (http://www.badastronomy.com/phpBB/viewtopic.php?p=93091&highlight=lageos#93091) last year. He said "the first detection of Lense-Thirring as dating to 1995, with
better results yet in 1998, with NASA releasing news of the detection at
least as early as January 1999"

dvb
2004-Sep-14, 10:16 AM
Why does it take them so long to complete these tests? :-?

scourge
2004-Sep-14, 10:24 AM
Princz had some info on it (http://www.badastronomy.com/phpBB/viewtopic.php?p=93091&highlight=lageos#93091) last year. He said "the first detection of Lense-Thirring as dating to 1995, with
better results yet in 1998, with NASA releasing news of the detection at
least as early as January 1999"

Thanks milli360, I'll have to track those articles down, unless someone 'round here has the numbers--I gotta say, the frame-dragging/Lense-Thirring phenomenon is one of the most fascinating areas of modern fundamental physics investigation. I can't wait to see how it all pans out, and what implications it all may hold for GR and Mach's Principle...at the boundaries of our models of reality, enticing new truths await discovery...

milli360
2004-Sep-14, 10:41 AM
dvb:
Why does it take them so long to complete these tests?
yeah, aren't they supposed to have them marked, graded, recorded and returned by the next class period?

antoniseb
2005-Mar-31, 07:10 PM
New Scientist has posted this interview
http://www.newscientist.com/channel/opinio.../mg18624931.300 (http://www.newscientist.com/channel/opinion/mg18624931.300)

With Francis Everitt, the head scientist behind Gravity Probe B, which was launched a year ago, and will return results in four or five months.

It gives some insight as to how this very long project came together, and what this guys life has been like. I enjoyed this interview quite a bit.

John L
2005-Mar-31, 08:17 PM
I've been following the mission since before it launched. I was really worried when the recent solar flare activity disrupted the probe, but thankfully they were able to fully recover. I can't wait for the final results of this and WMAP year 2, 3 and onward data.

antoniseb
2005-Mar-31, 08:34 PM
Originally posted by John L@Mar 31 2005, 08:17 PM
can't wait for the final results of this and WMAP year 2, 3 and onward data.
I agree. There are quite a few really good bits of information being processed at this time. I am anxious to see the results.

ToSeek
2005-May-12, 04:31 PM
Gravity Probe B mission, testing Einstein's theory of gravity, completes first year in space (http://www.physorg.com/news4062.html)


According to Einstein's 1916 general theory of relativity—our present theory of gravitation—space and time are inextricably woven into a four-dimensional fabric called spacetime, and gravity is nothing but the warping and twisting of spacetime by massive celestial bodies. Is this theory correct? The Gravity Probe B (GP-B) satellite recently completed its first year in orbit around the Earth and is continuing to collect data in the first controlled experiment specifically designed to answer this question.

A Thousand Pardons
2005-May-12, 04:59 PM
Happy Birthday B

antoniseb
2005-Jul-27, 03:25 PM
The Gravity Probe B website indicates that they will run out of Helium in the Dewar at the beginning of September. They have got about 48 weeks so far of being in science mode, and the final week or so will be the final callibration.

The website says the following about when the results will be published:


We are entering the final weeks of science data collection and preparing for the final instrument calibration tests before the helium in the Dewar is exhausted, sometime around Labor Day. At that point, the main focus of GP-B will shift from mission operations to data analysis. The painstaking scientific analysis work will require over a year to complete, followed by up to six months of preparing and submitting scientific papers to major scientific journals. This process will culminate in the announcement and publication of the results, now anticipated to occur in April 2007.

That's a long time from now, but at least it isn't as open ended as the WMAP year-two and polarization data.

Jerry
2005-Aug-08, 04:23 AM
April of 2007?

The mathematics of the gravity B probe are tough, but not that tough. More importantly, the algorythms for data reduction should have been finalized before the probe was even launched. Information on the B probe site intimated a much sooner release.

This should have been true for the WMAP Data reduction as well. When the PI's take years to do data analysis, all sorts of Von Engle factors can be pirated in that have the potential of reversing the true results of the experiment.

WMAP did this with the first release - changing the expected power function of the secondary peak by introducing new parameters - this occurred before the data collection was completed, but they changed the expectations because the Boomerang balloon had already demonstrated the secondary peak was highly constrained, in at least part of the sky. (http://lanl.arxiv.org/abs/astro-ph/0312570)

Personally, I expect affirmative results from the B-probe, but I would like to be more certain that the 'blind' checks that the PI's built into the analysis are followed. Two years of massaging data before it is released does not inspire confidence.

Jerry
2005-Oct-03, 03:16 PM
http://einstein.stanford.edu/

Mission Director Bob Kahn:



On Mission Day 528, the Gravity Probe B vehicle and payload are in good health, with all subsystems performing nominally. The Dewar is now depleted of liquid helium, and this has affected various subsystems, as summarized below. Drag-free mode has been turned off.

By every account this mission has been a complete success, but there are some interesting assides:


Analysis later this week showed that Monday's failed attempt was consistent with similar failures we had seen during the Initiialization and Orbit Checkout (IOC) phase of the mission in July and August, 2004, and it was likely due to un-modeled forces between the gyro rotor and its housing.


Unmodeled forces always get my attention, because this is where 'new science' emerges if and when all sources of error are eliminated.



Our science team is interested in comparing the data collected in science configuration during this past week with the science data they collected prior to beginning gyro torque calibrations in mid August.

Most of the time, once the dust has settled, the ambiguities are sorted out and there is order in the universe. What will this carefully engineers test of frame dragging reveal?

The final report of the Gravity Probe B team is a long ways out there: June of 2007 (!?).

antoniseb
2005-Oct-03, 03:42 PM
Thanks Jerry, The song to the tune of "American Pie" was kind of sad.

I get the impression that the mention of un-modelled forces was referring to the behavior after it started warming up. I don't think they're talking about 'new physics' here.

hhEb09'1
2005-Oct-03, 03:56 PM
I get the impression that the mention of un-modelled forces was referring to the behavior after it started warming up. I don't think they're talking about 'new physics' here.I think that's Jerry's point. :) They may think it's not new physics, but it's still a possibility, and for weird science junkies (moi maximum culpable), that's intriguing.

Jerry
2005-Oct-03, 07:54 PM
Thanks Jerry, The song to the tune of "American Pie" was kind of sad.

I get the impression that the mention of un-modelled forces was referring to the behavior after it started warming up. I don't think they're talking about 'new physics' here.

I don't think so - I think they are talking about the planned final calibration phase completed about a week before the liquid helium ran out. They identified a similar problem during the initial calibration phase.

Unmodeled forces introduce a difficult problem. Since this effect was not anticipated, there is in all probability, no built-in routine for isolating this unexpected parameter. As always, I would like to know more details - what type of calibration yielded an unexpected result? Is it limited to a single gyro? Does it correlate with any particular spacial orientation, such as a pass over the South Atlantic anomally?

Jens
2005-Oct-04, 05:08 AM
My impression from reading that article was that the "unmodeled forces" only affected one of the gyroscopes, and if so I think it's unlikely that this would have any significance in the grand scheme of things. My impression was that there was some engineering flaw that they hadn't taken account of, like many that gyroscope wasn't quite as perfectly spherical as it was supposed to be, or something along those lines.

ToSeek
2005-Oct-04, 03:30 PM
Data collection completed (http://www.spaceref.com/news/viewpr.html?pid=17960)


Almost 90 years after Albert Einstein first postulated his general theory of relativity, scientists have finished collecting data to put it to a new, different kind of experimental test.

NASA's Gravity Probe B satellite has been orbiting the Earth for more than 17 months. It used four ultra-precise gyroscopes to generate the data required for this unprecedented test. Fifty weeks worth of data has been downloaded from the spacecraft and relayed to computers in the Mission Operations Center at Stanford University, Stanford, Calif. Scientists have begun the painstaking task of data analysis and validation, which is expected to take approximately one year.

Jerry
2005-Oct-05, 01:53 AM
My impression from reading that article was that the "unmodeled forces" only affected one of the gyroscopes, and if so I think it's unlikely that this would have any significance in the grand scheme of things. My impression was that there was some engineering flaw that they hadn't taken account of, like many that gyroscope wasn't quite as perfectly spherical as it was supposed to be, or something along those lines.


As was the case during IOC, these issues could have been resolved with further experimentation and fine tuning the Attitude and Translation Control system (ATC). However, given the imminent depletion of the Dewar's helium supply, we decided to return the spacecraft to its stable science configuration (backup drag-free mode, locked on the guide star) and remain in this configuration until the helium ran out--

These - plural. I don't know if this means there were problems with more than one gyro, or that they didn't resolve the issue during IOC, or both. In an experiment where precision and accuracy are everything, I don't understand why they returned to the drag-free mode, rather than 'further experimentation and fine tuning.' Kill all the demons you can, while you can.

akirabakabaka
2005-Oct-11, 07:11 PM
Putting relativity to the test: was Einstein right? (http://www.physorg.com/news7143.html)

Good article discussing the gravity probe B experiment.

Even though it has become one of the cornerstones of modern physics, general relativity has remained the least tested of Einstein's theories. The reason is, as Caltech physicist Kip Thorne once put it: "In the realm of black holes and the universe, the language of general relativity is spoken, and it is spoken loudly. But in our tiny solar system, the effects of general relativity are but whispers."

akirabakabaka
2005-Oct-11, 07:20 PM
"The ping-pong-ball-sized gyroscope rotors, for example, had to be so perfectly spherical and homogeneous that it took more than 10 years and a whole new set of manufacturing techniques to produce them. They're now listed in the Guinness Database of Records as the world's roundest objects." :clap:

ToSeek
2005-Oct-11, 08:14 PM
ToSeeked (http://www.bautforum.com/showpost.php?p=571482&postcount=6)

Fortunate
2005-Oct-12, 08:17 PM
I think this is one of the most delicate experiments ever pulled off by the human race. It requires such precision.

Launch window
2005-Oct-13, 04:58 AM
very good mission

Vermonter
2005-Nov-20, 04:30 AM
Found a link on FARK.

http://science.nasa.gov/headlines/y2005/16nov_gpb.htm?list766847

Says that GP-B is all done gathering data...and now the scientists have to analyze it and figure out what's what.

Jerry
2006-Jan-23, 06:40 PM
http://einstein.stanford.edu/


Our main focus is analyzing the science data we have collected and finishing our final report to NASA. In this regard, our final report to NASA, which is over 450 pages long, is now in the final stages of completion. Our science data analysis is proceeding according to plan. We are in the process of analyzing approximately 1 terabyte (1,000 gigabytes) of data collected from the spacecraft. Two independent analysis teams here at GP-B are working on the data, frequently comparing their results for both quality control and to ensure the validity of the data analysis algorithms.

The main part of the data analysis is expected to be completed late this summer (July-August 2006).

That's about a two-month slip from earlier estimates. Reasonable.

Nothing new on the LIGO sites...other than webpage overhauls. The LIGO bodies should be very busy with Science Run 5 (SR5).

ToSeek
2006-Jul-11, 04:39 PM
NASA Gravity Probe B Mission Update 7 July 2006 (http://www.spaceref.com/news/viewsr.rss.html?pid=21294)


As of July 7, we are continuing to progress through Phase II of the data analysis process, which began at the beginning of March and is scheduled to run through late August 2006. During Phase II, our focus is on understanding and compensating for certain long-term systematic effects in the data that span weeks or months. The primary products of this phase will be monthly spin axis precession estimates for each gyro, as well as refined daily spin axis orientation estimates. In this phase, the focus remains on individual, rather than correlated gyro performance.

antoniseb
2006-Jul-12, 09:20 PM
9 Months to go.

Nonkers
2006-Jul-18, 12:31 AM
Since the effects they are looking for are essentially geocentricin nature, and since the proper derivation thereof was geocentric even though it used relativity, I expect that the numbers will not be fudged too much, if at all, and I expect the effects to be confirmed.

Nereid
2007-Apr-10, 06:57 PM
Gravity Probe B's initial science results will be publicly released in a few days' time (http://einstein.stanford.edu/).

Garth (A. Barber) (http://arxiv.org/find/astro-ph/1/au:+Barber_G/0/1/0/all/0/1) has compiled a succinct list of all published predictions of what the two key results from GPB will be (they're at the end of this thread (http://www.physicsforums.com/showthread.php?t=104694)).

If you have your own theories, that GPB will be testing, you've only got a few more days to make them public ('prediction' after the fact - a.k.a. 'postdiction' - isn't anywhere near to powerful).

ToSeek
2007-Apr-10, 08:21 PM
Moved from Astronomy to Space Exploration since we're talking about the results of a space mission (am willing to be persuaded otherwise, though).

publius
2007-Apr-10, 10:47 PM
Let me persuade.......... :) This is General Relativity and Gravitation, big time. This (assuming GR comes shining through) will be the first direct, local observer on the scene, verification of frame-dragging/gravitomagnetic effects (well, that can be debatable, I guess), along with geodetic precession, a strange effect of spatial curvature.

And note how much stronger the geodetic effect is compared to the gravitomagnetic precession -- 2 orders of magnitude!

Anyway, this will be a seminal notch in the belt of General Relativity.

-Richard

Jerry
2007-Apr-14, 04:59 PM
I've tried to come up with a prediction, but after reading about how much work has gone into 'recalibrating after the fact', I fear preconceptions of what the final data should look like can creep into the final numbers.

There is no question additional unanticipated massaging is necessary - the 'perfect' gyroscopes proved to have slightly viscous moments, and the pre-release paper titles indicate they had a harder-than-expected time determining the exact position of calibration stars. (Some of this subtended from using single quasars as absolute standards, a practice suspended in precision astrometrics.)

So the data reduction reported in the Gravity probe B status reports appears to be based upon sound physics. What remains to be seen is whether or not the 'GR signal' can be isolated from other sources of noise, and whether or not these can be legitimately assigned physical causality.

All that said, IAOTO there should be unanticipate effects upon the probe gyros and their spin rates that is best characterized as period functions of the distance of the earth and moon from the sun. Unfortunately, the precision measuring period was less than one year, so this curious result would be less than fully established.

Hopefully, the results will lead to more careful measurements of gravitational potentials within the solar system.

For the few of us that think Titan is covered with silicate sand and gravel, and in general, the Newtonian predictions of masses based upon orbital calculations are severly flawed, the only true test is to start using primary standards in planetary probes; and including instrumentation in outer solar system probes that can absolutely quantify the composition of the moons of the outer planets.

In order for these nonnewtonian predictions to be true, the noise levels - the absolute variance found in the Gravity B probe must be greater-than-expected...and this has already been confirmed to be true. The only question is if they are systemic.

...and I think the reported 'difficulty' in reducing the data has already reduced the expectations of this probe to where 'seminal notch' status is inappropriate. Remember, the PI's insisted that only data reduction routines formalized before the launch would be used to analyse the data. That didn't work.

Nereid
2007-Apr-14, 05:23 PM
I've tried to come up with a prediction, but after reading about how much work has gone into 'recalibrating after the fact', I fear preconceptions of what the final data should look like can creep into the final numbers.

[snip]Well, like most such endeavours these days, the team will be releasing all the raw data too (http://einstein.stanford.edu/)* ... so you may perform whatever analyses you wish on it.

I sometimes wonder, Jerry, about comments like these from you ... sweeping, broad, with a hint of some kind of skullduggery ... yet when the relevant teams do^ release all the raw data, it seems you neither mention that fact, nor take the trouble to perform your own analyses on it. Would it be appropriate for you, someday, to start a thread in BAUT's Conspiracy Theories section (so we could require you to defend all your specific, concrete claims)?

*"In addition to providing a first peek at the experimental results at the APS meeting, the GP-B team has released an archive of the raw experimental data. The data will be available through the National Space Sciences Data Center at the NASA Goddard Space Flight Center beginning in June 2007."

^For avoidance of doubt, not every team always releases all the raw data, even after a proprietary period.

publius
2007-Apr-14, 05:43 PM
Well, if I read it right, geodetic precession has been confirmed to
within 1% of GR's prediction, but the 2 order of mangnitude gravitomagnetic/frame dragging precession is still being worked on, and we'll have to wait until the end of the year when the complete analysis is done to get that.

-Richard

Jerry
2007-Apr-15, 03:23 AM
Well, if I read it right, geodetic precession has been confirmed to within 1% of GR's prediction, but the 2 order of mangnitude gravitomagnetic/frame dragging precession is still being worked on, and we'll have to wait until the end of the year when the complete analysis is done to get that.

The PR graphic on the geodetic released today looks very good:

http://einstein.stanford.edu/


Today, Everitt and his team are poised to share what they have found so far-namely that the data from the GP-B gyroscopes clearly confirm Einstein's predicted geodetic effect to a precision of better than 1 percent.

However, the frame-dragging effect is 170 times smaller than the geodetic effect, and Stanford scientists are still extracting its signature from the spacecraft data. The GP-B instrument has ample resolution to measure the frame-dragging effect precisely, but the team has discovered small torque and sensor effects that must be accurately modeled and removed from the result.
These are what I am most interested in: Do they provide subtle clues that something might be missing from the equation?



I sometimes wonder, Jerry, about comments like these from you ... sweeping, broad, with a hint of some kind of skullduggery ... yet when the relevant teams do^ release all the raw data, it seems you neither mention that fact, nor take the trouble to perform your own analyses on it. Would it be appropriate for you, someday, to start a thread in BAUT's Conspiracy Theories section (so we could require you to defend all your specific, concrete claims)?

There isn't any doubt in my mind researchers sometimes overstate the confidence levels, or miss-interprete their data because of their prior expectations. Last week's downward revision in the accuracy estimates of the Cosmic Infrared Background power function is a perfect example: http://arxiv.org/PS_cache/arxiv/pdf/0704/0704.1498v1.pdf

This does not mean the first round of estimates were bad science - but the willingness of the same team of researcher to downgrade their original estimates made several years ago is definitely good science!

^For avoidance of doubt, not every team always releases all the raw data, even after a proprietary period.
For this (and most) space-based experiments, we almost have to rely upon the competence of the investigative teams. There is so much merging of engineering and science in this experiment and every parameter is so critical, it is virtually impossible for a third party to approach the raw data in a completely independent way.

Fortunately, there are a lot of reasons to expect fair interpretations from the G-probe B team of researchers-they have been very candid about the performance of their satellite. What I like most, is this quote in the press release from principle investigator:


The experiment’s final result is expected on completion of the data analysis in December of this year. Asked for his final comment, Francis Everitt said: "Always be suspicious of the news you want to hear."
I could not have stated it better myself.

Jerry
2007-Apr-15, 06:22 PM
Gravity B probe Executive Summary: (Nice history of the mission & guts and stuff, but no science)

http://einstein.stanford.edu/content/exec_summary/GP-B%20PFA%20Report-Pref-ExecSum-scrn.pdf

I find the poster on the gyroscope polhode moment very fascinating:


The polhode period of each gyro was observed to be changing over time. Each of the four exhibited similar asymptotic behavior. The only explanation that agrees with all the observation was that of energy dissipation in the rotor body. Dissipation moves the spin axis towards the maximum inertia axis where energy is minimum.

It is a reasonable explanation, but remember, they studied these gyroscopes for decades and never detected any viscous effects. Why did they suddenly show up in microgravity? To account for this effect, they had to add another term to the standard Euler equation.

Again, everything in this poster appears reasonable, but I still have to ask myself if these gyros should have enough internal viscous movement to cause the dampening, because the Earth-based tests said they do not. Remember, the rotational moments of both Pioneer probes dampened much more quickly than expected, and there is currently no explanation for this dampening. For those of us looking for good alternate theories of gravity, these may be important clues. Now I need to figure out how to compare the 'M shaped" frequencies observed in this orbiting probe with tidal charts for the same period...

publius
2007-Apr-16, 03:13 AM
Jerry,

By saying they added terms to the Euler equation, you're making it sound like they just pulled new physics out of some bodily orifice. What is the Euler equation, it is

I*dw/dt + w x L = T, the torque.

For zero applied torque, that describes the precession, or wobble of a rotating body when w is not parallel to L. When there is no torque, the right hand side is zero. When there is torque, the right hand side is equal to that torque.

What the GP-B team did was simply add a term for the torque. This is a blog by a writer who attended the conference:

http://twistedphysics.typepad.com/cocktail_party_physics/

Everritt said the problem was they modelled the electrostatic "patch effect" on the rotor, but *forgot about the housing* as he put it, according to the above author.

There was nothing there but an *unexpected* classical torque on the gyros that they had not anticipated. And if you'll read all the information on this incredible, unbelievable precise gyro, control, and measurement system, you'll see there were a lot of other torques on the gyros they were aware of and were ready for. Considering this was the first launch and operational test of this system, one can only marvel at how well they did model and anticipate all the effects they would encounter. Because this additional effect that had not anticipated, it could look like the signal they were looking for, which is why they were so meticulous about checking it out.

And all of these effects are so incredibly small relative to what we think is significant that it blows you away. The change in rotational energy due to the patch-drag was 10^-13W.

-Richard

Jerry
2007-Apr-16, 03:41 PM
Yes, the addition of the term in the Euler equation is reasonable, and so are the explainations. But they are applying new calibration factors that were not anticipated, and are based upon deviations from the expected results.

The team argues this is possibly the most technically difficult experiment ever conducted, and I agree.



Two important discoveries were made while analyzing the gyroscope data from the spacecraft: one, the "polhode" motion of the gyroscopes dampens over time; two, the spin axes of the gyroscopes were affected by small classical torques. Both of these discoveries are symptoms of a single underlying cause: electrostatic patches on the surface of the rotor and housing. Patch effects in metal surfaces are well known in physics and were carefully studied by the GP-B team during the design of the experiment to limit their effects. Though previously understood to be microscopic surface phenomena that would average to zero, the GP-B rotors show patches of sufficient size to measurably affect the gyroscopes' spins.

The gyroscope's polhode motion is akin to the common "wobble" seen on a poorly thrown American football, though it shows up in a much different form for the ultra-spherical GP-B gyroscopes. While it was expected that this wobble would exhibit a constant pattern over the mission, it was found to slowly change due to minute energy dissipation from interactions of the rotor and housing electrostatic patches. The polhode wobble complicates the measurement of the relativity effects by putting a time-varying wobble signal into the data.

The electrostatic patches also cause small torques on the gyroscopes, particularly when the space vehicle axis of symmetry is not aligned with the gyroscope spin axes. Torques cause the spin axes of the gyroscopes to change orientation, and in certain circumstances, this effect can look like the relativity signal GP-B measures. Fortunately, the drifts due to these torques have a precise geometrical relationship to the misalignment of the gyro spin/vehicle symmetry axis and can be removed from the data without directly affecting the relativity measurement.

Both of these discoveries first had to be investigated, precisely modeled and carefully checked against the experimental data before they could be removed as sources of error.


That's two unexpected parameters, both of which have been precisely modeled, and they are still crunching on the data, and do not expect to complete the analysis for another nine months. The question is, how many more post-facto parametric adustments will be necessary? If in the final analysis, they were to say 'Einstein was wrong'; the general community would look at the parametric breeding and say 'the experiment lacked proper controls'.

For those of us predicting the results should contain unexpected parametric swings, the question has to be ask: Are the explanations for the unexpectations arrived upon by the team the only reasonable answers?

Another way to state this, is if it is ALWAYS assumed only known physics are in play, how could we ever recognize true deviations? Once again, let me be the Devil's advocate:

The periodic and random changes in the probe housing relative to the test mass are a direct response to the local atmosphere, gravity fields, lunar orbits and so on. The gyroscopes are supposed to be isolated from these reorientations, only deviating when 'space itself' is altered. But what if the response of the gyros is a direct, unexpected effect upon both the gyro and the housing, not coupled to the gyros from the housing by electrostatic patches? These are the uncontrolled conditions that crop up when a unexpected, uncalibrated, correction is required. The more unexpected parameters that are needed, the higher the probability that the initial assumptions are flawed.

When the Mars Phoenix probe falls faster-than-expected next year, for the tenth straight time, will it be blamed upon three sigma variations in the atmosphere?

Nereid
2007-Apr-16, 04:52 PM
But Jerry, with very few exceptions, we all do processing of all astronomical (and 'physics in the lab') work, all the time!

Take any modern instrument: it's built according to certain theories, tested according to those theories, and used to make observations (experiments) within the framework of those theories.

How could it be otherwise?

And as for testing results such as those from GPB, within the framework of some new idea, well, sometime later this year the team will release all the raw data ... so you can do whatever analyses you wish on it (just as, IIRC, the COBE and WMAP teams also released all the raw data too).

Surely the best way to demonstrate an alternative is to actually work one out, in quantitative form? Then publish it, and show, from analysis of the raw data, that it is consistent?

Jerry
2007-Apr-16, 06:12 PM
But Jerry, with very few exceptions, we all do processing of all astronomical (and 'physics in the lab') work, all the time!

Take any modern instrument: it's built according to certain theories, tested according to those theories, and used to make observations (experiments) within the framework of those theories.

How could it be otherwise?

Absolutely correct.

The problem here is, the G-Probe B scientists cannot bring the shell down and confirm that there are magnetic 'patches' in the supporting framework that are causing unexpected deviations. Likewise, they cannot confirm there is a viscous element in each of the gyroscopes that they failed to observe in two decades of ground-based testing.


And as for testing results such as those from GPB, within the framework of some new idea, well, sometime later this year the team will release all the raw data ... so you can do whatever analyses you wish on it (just as, IIRC, the COBE and WMAP teams also released all the raw data too).

Surely the best way to demonstrate an alternative is to actually work one out, in quantitative form? Then publish it, and show, from analysis of the raw data, that it is consistent?
No, I cannot - because I cannot test their assumptions that tie the unexpected behavior to unproven initial conditions - we would have to bring the probe back, and see if the gyroscopes really do have a viscous moment and so on.

The same is true of the WMAP data: When the second and third year data did not properly overlay the first year, they re-examined their thermal modeling, least-square-fitted the results to minimize the variance and declared victory.

Yes, these are proven technics used by scientists to go back over the data and correct for systemic errors after the testing, but there is always danger when there is no way to confirm the assumption independently. This is why the Gravity-B probe scientists made a big point of the fact (before the testing) that the analysis package was mature; and would not have to be modified to interpret the data.

http://einstein.stanford.edu/highlights/hlindexmain.html



By design, the spin axes of the gyroscopes are aligned with the axis of the telescope, which is also the roll axis of the spacecraft, and as long as these alignments are maintained, the non-relativistic torques on the gyros average out. However, during these final calibrations, we intentionally break these alignments, forcing the telescope first one degree and then seven degrees away from the gyro spin axis alignments, and we can then determine the extent to which these misalignments place torques on the gyro spin axes. Clearly, given the nature of these final calibration tests, they could not be performed while we were still collecting science data, which is why they were left to be performed at the very end of the experiment.

Reading between the lines, it was during this final calibration that the evidence of the 'patch effect' emerge, so they do have a pretty good method for nulling this unexpected source of error. Great experiment! Great, puzzling results!

Jerry
2007-Apr-17, 04:27 PM
Surely the best way to demonstrate an alternative is to actually work one out, in quantitative form? Then publish it, and show, from analysis of the raw data, that it is consistent?
It should be.

In the current enviroment, I do not believe this is possible: There are two mutually exclusive theories that are completely accepted: GR and QED or QCD. I don't think you can seriously tweak one without violating the other, and no one has pulled together a viable combined theory. That is the paradox.

A new standard theory requires a new set of standard assumptions; then tests designed specifically to test the new assumptions. As long as the known discrepancies between current theory and observations are given black box status, new theories cannot grow. It's a twelve step problem, and the first step is admitting something is fundamentally wrong.

dcolanduno_old
2007-Apr-18, 02:51 PM
http://news.bbc.co.uk/2/hi/science/nature/6561391.stm

antoniseb
2007-Apr-18, 03:07 PM
Yes, You'll see the other threads with GPB in the title.

NEOWatcher
2007-Apr-18, 03:13 PM
http://news.bbc.co.uk/2/hi/science/nature/6561391.stm

If you're so sure, then why make the post?

For those wondering... Preliminary results of Gravity probe B.

Anyway, it's been discussed a lot (here's a google (http://www.google.com/search?hl=en&q=+site:www.bautforum.com+%22bad+astronomy%22+%22g ravity+probe%22))

Most of the story is old news, the rest is preliminary, so it doesn't sound too noteworthy to me. More like a reporter asking a physicist what they are working on.

And a request: Please explain what a post is so we don't have to go walking around the web to find out what you are talking about.
We don't want to be the victim of a malicious link...
Edit: Did I not reat the entire thread title? Oops.

ToSeek
2007-Apr-18, 03:26 PM
Threads merged, with a redirect.

Jerry
2007-Apr-19, 11:43 PM
In one of the Gravity=B Posters, there is a correction for 'Annual Aberration', the dominant component τˆ

http://einstein.stanford.edu/

"Classical Torques on Gravity Probe B Gyroscopes"

Does anyone know what causes this? Is it an atmospheric correction? That seems a bit high for the GP-B orbit.

Nereid
2007-Apr-27, 12:44 PM
[snip]

When the Mars Phoenix probe falls faster-than-expected next year, for the tenth straight time, will it be blamed upon three sigma variations in the atmosphere?Let's hope that the mission planners use more data (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006DPS....38.7302T&db_key=AST&d ata_type=HTML&format=&high=41e090e48232390)-driven (http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006JGRE..11109S04Q&db_key=AST&d ata_type=HTML&format=&high=41e090e48210803) atmospheric models whose development has been made possible by observations not available to earlier mission operators.

Nereid
2007-Apr-27, 12:57 PM
But Jerry, with very few exceptions, we all do processing of all astronomical (and 'physics in the lab') work, all the time!

Take any modern instrument: it's built according to certain theories, tested according to those theories, and used to make observations (experiments) within the framework of those theories.

How could it be otherwise?Absolutely correct.

The problem here is, the G-Probe B scientists cannot bring the shell down and confirm that there are magnetic 'patches' in the supporting framework that are causing unexpected deviations. Likewise, they cannot confirm there is a viscous element in each of the gyroscopes that they failed to observe in two decades of ground-based testing.
And as for testing results such as those from GPB, within the framework of some new idea, well, sometime later this year the team will release all the raw data ... so you can do whatever analyses you wish on it (just as, IIRC, the COBE and WMAP teams also released all the raw data too).

Surely the best way to demonstrate an alternative is to actually work one out, in quantitative form? Then publish it, and show, from analysis of the raw data, that it is consistent?No, I cannot - because I cannot test their assumptions that tie the unexpected behavior to unproven initial conditions - we would have to bring the probe back, and see if the gyroscopes really do have a viscous moment and so on.

The same is true of the WMAP data: When the second and third year data did not properly overlay the first year, they re-examined their thermal modeling, least-square-fitted the results to minimize the variance and declared victory.

Yes, these are proven technics used by scientists to go back over the data and correct for systemic errors after the testing, but there is always danger when there is no way to confirm the assumption independently. This is why the Gravity-B probe scientists made a big point of the fact (before the testing) that the analysis package was mature; and would not have to be modified to interpret the data.

[snip]As GPB is the only 'experiment' of this kind currently, or planned, there is a risk - albeit small - that some aspect of the experiment renders this particular test weaker than it should be.

The usual approach, in science, is independent validation, via repetition, with a design that is also independent ... and for the CMB we have oodles of just such (http://background.uchicago.edu/~whu/cmbex.html), with one of the best still to come (Planck (http://www.rssd.esa.int/index.php?project=Planck)).

I'm still puzzled at your apparent unwillingness to even try to get a serious alternative off the ground. After all, at least 13 others (http://www.physicsforums.com/showpost.php?p=1307650&postcount=174) managed to get quite specific predictions published before the first scientific GPB results were announced.

Gsquare
2007-Apr-28, 03:00 AM
In one of the Gravity=B Posters, there is a correction for 'Annual Aberration', the dominant component τˆ

http://einstein.stanford.edu/

"Classical Torques on Gravity Probe B Gyroscopes"

Does anyone know what causes this? Is it an atmospheric correction? That seems a bit high for the GP-B orbit.

Hello, Jerry. I don't see any "aberration" you referred to in the "Classical Torque...." post..... Perhaps you can pin it down within the post with a page number.

Nevertheless, to explain...
There are two components of starlight aberration that must be subtracted in the GP-B data reduction, both to account for aberration corrections as perceived by the on-board 'guide star' tracking telescope.

The first is the aberration due to its earth's orbit, which amounts to about (I think) +/-5.5 arc-sec. in the orbital plane...and was originally derived from sat. tracking data .

The other (greater) component (annual aberration) is due to the earth's orbital motion about the sun, ~ (20 arc-sec. or so?) .
The amount is known very accurately from the JPL ephemerides to ~0.06 milliarc-sec.

Both signals are superimposed upon and distinguishable from relativistic effects because they possess well known amplitude & phase.

Show me where it is located in the link (and in the post) and I will expand a little.

G^2 :D

BTW, I do agree it is somewhat disconcerting to see new error parameters (Polhode & Patch) introduced after the fact.
My guess is that it will degrade the accuracy of the 'frame dragging' measurement an order of magnitude or so....after the full reduction of data.

Referring to it as a 'New' discovery is like calling the flat tire on my car a 'new discovery' to the occupants who I am taking to dinner. :D I'm sure you realize in this business putting a positive spin on things and 'using' setbacks for advantage is often neccessary for survival. ;)

..

Gsquare
2007-May-01, 03:26 AM
Gravity Probe B's initial science results will be publicly released in a few days' time (http://einstein.stanford.edu/).

Garth (A. Barber) (http://arxiv.org/find/astro-ph/1/au:+Barber_G/0/1/0/all/0/1) .... has compiled a succinct list of all published predictions ....



Nereid;
Are you subscribing any validity to Garth's proposal? I haven't had time to go through it but....
....I really don't see why Garth Barber , (and others) can expect 'Creation Cosmology' theory to be viable when it predicts 2/3 of the GR goedetic results. Even prior to GP-B results, the geodetic effect (in Gen. Rel.) has been met to within 1% (as pointed out by Richard), and I believe could even be considered to be within 0.1 % using Shapiro time delay.

Am I missing something?

G^2

Nereid
2007-May-01, 07:37 AM
Nereid;
Are you subscribing any validity to Garth's proposal? I haven't had time to go through it but....
....I really don't see why Garth Barber , (and others) can expect 'Creation Cosmology' theory to be viable when it predicts 2/3 of the GR goedetic results. Even prior to GP-B results, the geodetic effect (in Gen. Rel.) has been met to within 1% (as pointed out by Richard), and I believe could even be considered to be within 0.1 % using Shapiro time delay.

Am I missing something?

G^2Not at all ... it's just that, in that thread, he put together, in a single post, a list of the dozen or so specific (non-GR) predictions for the two GR-related results that GPB will report on/has reported on*, published before the first results were released (naturally, GR is #1 on the list).

You'll see that his own predictions - and so SCC - don't fit with the results.

In fact, five of the original 13 (http://www.physicsforums.com/showpost.php?p=1307650&postcount=174) have already bitten the dust.

Of the remaining eight, which includes GR, three (possibly four or five) could be ruled out by year end.

*So far, there's one of each.

publius
2007-May-01, 06:14 PM
I'll point at that Robertson's "Newtonian Gravity Theory" is actually just almost straight GEM, or a Heaviside-like gravity from the Maxwell analog. There is a a factor of 4 on the gravitomagnetic factors that comes out of GR's, well "fancy stuff". That factor of 4 would not be on a straight Maxwell-like gravity.

You get deduce that gravitomagnetic effects must be present from a simple thought experiment of considering a charged mass system in equilibrium where gravitational attraction just cancels electric repulsion. Now, watch that from a moving frame. If there are B effects, which can be seen an SR effect on the Coulomb field (in this case), there must a similiar effect on gravity. And indeed there must similiar magnetic-looking effects on *any force*. Take a spring and have the compression cancel electric attraction. The spring force must have an SR magnetic-like velocity dependent component as well.

Doing that by straightfoward means gets you Heaviside's original GEM like gravity. And that is wrong. :) Basically it violated the equivalence principle because the gravitational "charge" (mass) is different from the inertial mass. Keeping those the same gets you GR and that factor of 4. It's complicated, and don't ask me to show it. :)

Actually, I think that factor of 4 (which is 2 applied twice, once on source, once on receiving mass) comes from the same thing that puts a factor of 2 on the Newtonian potential in g_00, ie g_00 = 1 - 2GM/r (think of the 1 there as a "gauge" term that makes it 1 at infinity rather than 0, which it has to be because that's the stationary clock rate in that coordinate system).

Anyway, Robertson thought it would be interesting and useful to do the straight Heavside/no factor of 4 predictions for GPB.

ETA: The above mass-charge equilibrium illustrates why gravity has to be so complicated. Do it naively by SR considerations alone, think you've done something, then you realize you've violated the Equivalence Principle. The reason is that inertial mass, to the moving observer increases by a factor of gamma (well, in the transverse case, it's more complex), but you said the gravitational mass, being analgous to charge, was just the rest mass.

That conundrum is why gravity cannot be a mere vector field in the general case. Only a tensor field can be made to work out in all cases and have the Equivalence Principle hold and still have inertial mass appearing to increase with velocity.

This is why gravity is so darned complex.

-Richard

ToSeek
2007-May-01, 09:40 PM
Will Gravity Probe B fulfill its promise? (http://www.newscientist.com/blog/space/2007/04/will-gravity-probe-b-fulfill-its.html)


In April 2007, the project released some good news and some bad news (http://space.newscientist.com/article/dn11615-gravity-probe-measures-earths-dent-in-spacetime.html). Electrostatic effects called "charge patches" caused unexpected torques on the gyroscopes and thus noise in the data. The good news is that the current measurement noise is at the level of 0.1 arcseconds, so the geodetic effect was confirmed to about 1%. But the bad news (and the main project reason for building such an accurate instrument and putting it in orbit) was to measure frame-dragging, which is impossible to see in the current state of the data.

As mission leader Francis Everitt says on NPR's All Things Considered (http://www.npr.org/templates/story/story.php?storyId=9682351), the measurements are now 1000 times less precise than what they expected. Careful modelling may regain a factor of 100 by December.

CJSF
2007-May-01, 09:47 PM
Can they re-run any tests now that they know about the charge patches to either get better data, or help reduce the noise?

CJSF

Gsquare
2007-May-02, 03:42 AM
Will Gravity Probe B fulfill its promise?

As mission leader Francis Everitt says on NPR's All Things Considered, the measurements are now 1000 times less precise than what they expected. Careful modelling may regain a factor of 100 by December...
(http://www.newscientist.com/blog/space/2007/04/will-gravity-probe-b-fulfill-its.html)

Thank you ToSeek; Uncertainty in modeling of the patch error not only will degrade the accuracy of Gravitomag. measurement, but is also certainly going to reduce the confidence levels of the data, making any comparison with competing theories (that rely on gravitomagnetic differences) suspect and maybe even marginal at best.

All this may actually be a moot point since other recent reports from lunar ranging by Nordtvedt (using 35 years of lunar laser ranging data) have confirmed gravitomagnetism in the earth-moon system to 0.1 % of the GR prediction.

See here:
http://arxiv.org/PS_cache/gr-qc/pdf/0702/0702028v1.pdf

Nordtvedt has been at the forefront for years in LLR, and (although not given the publicity of more media hyped GP-B) has previously shown that the solar geodetic effect (the so-called deSitter-Folker precession which rotates the plane of the earth-moon system), confirms GR predictions to about the same accuracy (0.1 %), ......and has also put tight constraints on competing theories, (as well as confirming the non-linear coupling of earth's gravity to itself, and the constancy of G to high precision).

See here;
http://www.springerlink.com/content/2gjffbwea99mrjxa/

Needless to say, Everitt was not too happy about the Nordtvedt report on Gravitomagnetism....but the same GR gravitomagnetic term that is used for the GP-B frame dragging is also responsible for the Gravitomagnetism of two rotating massive objects.

So why not use the 'God given' gyroscopes that are already in place ? ....dang, Nordtvedt didn't even have to make the moon go superconducting or polish it to one billionth of a cm. ! :D

G^2 :D

publius
2007-May-02, 04:42 AM
G^2,

If I read that .pdf right, the moon's orbit deviates no more than roughly 1cm from GR's predicted course. If that's correct, then that is darn-tootin' good.

And from the Springerlink abstract, another thing I like is the earth and moon fall toward the sun at the same rate to within 10^-13. That is pretty good, too.

-Richard

-Richard

Gsquare
2007-May-02, 02:25 PM
G^2,

If I read that .pdf right, the moon's orbit deviates no more than roughly 1cm from GR's predicted course. If that's correct, then that is darn-tootin' good.

-Richard

Yep, darn-tootin'; the accuracy of LLR is apparently down to a couple of mm.

G^2

Gsquare
2007-May-04, 05:24 AM
...... gravitomagnetic effects must be present from a simple thought experiment of considering a charged mass system in equilibrium where gravitational attraction just cancels electric repulsion.



True;
Good point that 'any force' binding them will also require a vel. dependent term in the moving frame.





(In) The above mass-charge equilibrium ............... you realize you've violated the Equivalence Principle. The reason is that inertial mass, to the moving observer increases by a factor of gamma....., but you said the gravitational mass, being analgous to charge, was just the rest mass.


I'm not so sure about that.....
To the moving observer there is also Length contraction (in the direction of motion) by the same factor gamma; the shortened length between masses means greater gravitational mass. Also the charge density increases by a similar amount due to the same length contraction....so its possible mass-charge stays in equiibrium;(haven't done the math though).

G^2 ;)

publius
2007-May-04, 06:04 AM
I'm not so sure about that.....
To the moving observer there is also Length contraction (in the direction of motion) by the same factor gamma; the shortened length between masses means greater gravitational mass. Also the charge density increases by a similar amount due to the same length contraction....so its possible mass-charge stays in equiibrium;(haven't done the math though).
G^2 ;)

That's a tricky thing. The charge density (and current density) is frame dependent, but the total charge is invariant. Mass-energy is not invariant, and that is the difference. A sphere in the rest frame gets "squashed" looking in the moving frame, with the charge density and the E-field looking different accordingly, but the total charge is invariant.

Here is a paper that goes into detail on the mass-charge equilibrium:

http://www.arxiv.org/abs/gr-qc/0304084

Note the interesting thing. If you add the requirement that inertial mass equal gravitational mass, you get only one factor of 2 (to first order, there are higher order terms apparently) on the gravitomagnetic force. The authors say the other factor of 2 can be seen as coming from "curvature". :)

Note that Maxwellian gravity (without the factor of 4) would be completely Lorentz-kosher otherwise. It's only if you require the Equivalence Principle to absolutely hold that things have to get fancy........ :)

-Richard

Gsquare
2007-May-08, 10:25 PM
That's a tricky thing. The charge density (and current density) is frame dependent, but the total charge is invariant.


Yes, of course; not thinking. :doh: And thus it has become a 'nicht gedenken' experiment. :)



Here is a paper that goes into detail on the mass-charge equilibrium:

http://www.arxiv.org/abs/gr-qc/0304084



Yes, Richard; thanks for pointing that out; that is the very reference I gave you a few months ago when we were discussing the interaction of gravitomagnetism with spin, and how it must imply EP violation,....remember here: http://www.bautforum.com/showthread.php?t=39692&page=3&highlight=gravitomagnetism (in post #78; concerning Tajmar & deMatos experimental detection of the Gravitomagnetic field of a spinning superconductor).

However, I unintentionally skipped over the section on justification of Gravitomagnetism using this thought exp.( :doh: ), since my intention was to focus on the implications of the Maxwellian gravity analogs involving spin, and not proving the necessity of gravitomagnetism, (However, the author does give a good formal presentation.). I really liked his approach since it uses the linear differential form of the gravitational field analogs which are heuristically simpler and more amenable to my limited cognitive resources. ;) Nevertheless, as far as I am concerned there is enough 'real' physical evidence for gravitomagetism (GP-B not withstanding), that I need not resort to 'gedenken' type simplifications.

That is what my 'Nordtvedt post' above was about. Gads; Nordtvedt even makes the case that gravitomagnetism is quite ubiquitous .... in the origin of inertia....:eek:

Here is a very interesting secondary source...referring to his comments ....
http://physics.fullerton.edu/~jimw/general/inertia/nord.htm
You are probably already familiar with it; if not, I recommend it considering the implications.

Nevetheless, I really do want to get back to the issue of gravitomagnetism coupling to spin since that is where the experimental evidence is lacking.

Maybe I will resurrect our last discussion in that regard when I have more time.

G^2 :D

Jerry
2007-Sep-26, 06:56 PM
http://einstein.stanford.edu/



One of the intriguing puzzles at an earlier stage of the analysis was that the clocking of the gyroscope housings with respect to the rolling spacecraft frame appeared to vary with time, and from gyro to gyro, in a manifestly unphysical way. In other words, the rolling spacecraft is like a flywheel, and the gyro readout planes are very stably locked to it, so there cannot be any physical variations, yet, such variation appeared to be present in the data.

Fortunately, the improved polhode phase determinations have effectively eliminated this apparent variation. Moreover, this modeling and estimation of the misalignment torque coefficient, which constitutes the main disturbance of gyro motion, has now been improved by a factor of five.

Unfortunately, there is no way on Earth to confirm that a time-variant polhode moment is the proper solution. One expects the polhode moment of an egg to vary over eighteen months, but not a set of spheres made from materials chosen because of their known (presumed?) stability. It would seem to be a worthwhile test of the varacity of this 300,000,000+dollar assumption to construct a duplicate set of spheres and see if the polhode properties on earth are the same as they are in the heavens.

Jerry
2007-Oct-05, 06:52 PM
Testing for Lorentz Violation: Constraints on Standard-Model Extension Parameters via Lunar Laser Ranging
James B. R. Battat, John F. Chandler, Christopher W. Stubbs
Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138

http://arxiv.org/PS_cache/arxiv/pdf/0710/0710.0702v1.pdf


We present constraints on violations of Lorentz Invariance based on Lunar Laser Ranging (LLR) data. LLR measures the Earth-Moon separation by timing the round-trip travel of light between the two bodies, and is currently accurate to a few centimeters (parts in 1011 of the total distance). By
analyzing archival LLR data under the Standard-Model Extension (SME) framework, we derived six observational constraints on dimensionless SME parameters that describe potential Lorentz violation.

We found no evidence for Lorentz violation at the 10−6 to 10−11 level in these parameters.
New constraint, by at least one full magnitude. This methodology assumes that the speed of light is constant in order to make the measurement; so it is not a perfect test of relativity. It does eliminate or severely constrain many alternatives.

After looking at some of the modifications they are making in the APOLLO experiment, such as measuring the effects of continental drift, it will be interesting to see how much the moon's orbital path is truly increasing. First round APOLLO science testing should be completed within a year.

Jerry
2007-Oct-09, 03:13 PM
Constraining Torsion with Gravity Probe B
Mao, Tegmark, Guth and Cabi

http://arxiv.org/PS_cache/gr-qc/pdf/0608/0608121v4.pdf


It is well-entrenched folklore that all torsion gravity theories predict observationally negligible torsion in the solar system, since torsion (if it exists) couples only to the intrinsic spin of elementary particles, not to rotational angular momentum. We argue that this assumption has a logical loophole which can and should be tested experimentally, and consider non-standard torsion theories in which torsion can be generated by macroscopic rotating objects.
OK, that is a legitimate premise: If a torsion gravity theory is correct, One would expect this hypothetical angular momentum coupling to be time variable; that is, to effect the rotational moments of the Gravity B probe.

We know the rotational moments of the Gravity B probes did change over time, and this unexpected change is thought to be due to electrostatic coupling and a time-dependent Polhode moment. If this unexpected momentum is due to torsion coupling; The coupling of each gyroscope should vary as a function of the angle of the gyroscope relative to the local 'torsion' moment. It would be interesting to see what the net Polhode correction would be if the torsion correction is first applied to each gyroscope.

Jerry
2007-Dec-11, 04:52 AM
http://einstein.stanford.edu/



In our September 25, 2007 status update, we reported that the trapped flux mapping technique had resulted in a dramatic improvement in the determinations of the polhode phase and angle for each gyroscope throughout the entire 353-day experiment period. Applying these results to a central 85-day stretch of data, from December 12, 2004 through March 4, 2005, we obtained a robust and stable measurement of the frame-dragging effect with a reasonable (~30%) error level. We are in process of progressively extending the analysis to increasingly long time intervals in order to reach the full experiment accuracy, potentially to an error margin of less than 5%. Also important is the completion of the study of—and if necessary elimination of—any remaining systematic effects that may bias the results of the experiment.

So...when you use a "trapped flux mapping technique", how do you know how much of the deviation is due to unexpected flux, and how much is honest-to-goodness deviation in the experimental result from what was expected?

Gsquare
2007-Dec-12, 04:00 AM
http://einstein.stanford.edu/



So...when you use a "trapped flux mapping technique", how do you know how much of the deviation is due to unexpected flux, and how much is honest-to-goodness deviation in the experimental result from what was expected?


Good question...probably you don't know.
I really don't put much confidence in "tweaking" the gravitomagnetic data with new 'ad hoc' experimental models ....it seems too much like someone's trying to fit the data so as to resurrect a GR prediction from the GP-B ashes...

If 30% error level is considered "reasonable" then the Lageos satellite detection by Ciulfolini beat them to the punch, at least for the gravitomagnetic part.

Maybe we should go back and investigate other approaches....like the South Pole gravitomagnetic proposal by Braginsky and Kip Thorne.

Rather than divert the OP I've put that idea on another thread here:

http://www.bautforum.com/astronomy/67983-south-pole-experimental-detection-gravitomagnetism.html#post1131522

G^2 :D

ToSeek
2008-Jan-17, 04:18 PM
Has Gravity Probe B been a Big Flop? (http://www.scienceblog.com/cms/has-gravity-probe-b-been-big-flop-15250.html)


Although the Wikipedia article on the geodetic effect states that it has been confirmed to the 1% level, there is evidence that the best value that they obtained are not in agreement with Einstein's GR! This NASA/Stanford slide: http://colloquia.physics.cornell.edu/11-12-2007/cornellpres_files/v3_sli...
is showing that to a 1 sigma error confidence level the results for the geodetic precession are inconsistent with GR.

There were two unexpected sources of error affecting the gyros that almost ruined the whole effort, but the project scientists are confident that they can filter out the errors and reveal the true data. They are still struggling with the geodetic effect, never mind the very much smaller frame dragging effect.

So what if this whole effort turns out one big waste of money, with no clear result?

antoniseb
2008-Jan-17, 05:42 PM
what if this whole effort turns out one big waste of money, with no clear result?
Then it will be like LIGO which has taught researchers more items they need to study and resolve to be able to successfully measure this kind of thing.

I'm thinking that Gravity Probe C should be in a low orbit around Jupiter.

Swift
2008-Jan-17, 06:16 PM
As I'm fond of saying, "if we knew what we were doing, it wouldn't be called research". ;)

alainprice
2008-Jan-17, 07:08 PM
I still have high hopes for this experiment.

It's a shame that so many decades of work might end up with inconclusive results.

hhEb09'1
2008-Jan-18, 12:16 AM
Has Gravity Probe B been a Big Flop? (http://www.scienceblog.com/cms/has-gravity-probe-b-been-big-flop-15250.html)As near as I can tell, the graph that he is referring to is #36 of Cornell Colloquia for Nov. 12 (http://colloquia.physics.cornell.edu/11-12-2007/cornellpres_files/frame.htm). Frame #2 is a nice overview. But #36 seems to say that the measured frame-dragging effect is -82 +/- 13, and general relativity predicts -75. The measured geodetic effect is 6632 +/- 43, and the predicted is -6571 (taking into account, the earth, sun, and proper motion), which are of course less than one percent off in both cases. Much less than one sigma in the first case, less than 1.25 sigma in the second. The graph is just saying that they believe the accuracy of their measurements is very tight--but given the discussions, maybe they have some system errors yet to discover. I wish I got as good of results :)

mantiss
2008-Jan-19, 09:53 PM
I'm thinking that Gravity Probe C should be in a low orbit around Jupiter.


That would require radiation shielding a few kilometers thick no? But seriously much more hardened than say Galileo was.

antoniseb
2008-Jan-19, 10:40 PM
...much more hardened than say Galileo was.
Agreed on the necessity for thick shielding, though that is just to get it there. I'm thinking that like Earth, there are orbits below the radiation belts that would work just fine.

Jerry
2008-Jan-20, 12:56 AM
Given the extensive massaging of the data to remove unexpected 'effects'; it would be impossible to use this data to constrain a theory that predicted modest deviations from GR. We knew that 650 million dollars before this mission.

antoniseb
2008-Jan-20, 01:46 AM
Given the extensive massaging of the data to remove unexpected 'effects'; it would be impossible to use this data to constrain a theory that predicted modest deviations from GR. We knew that 650 million dollars before this mission.
Do you think that enough information was collected to enable doing it better next time?

alainprice
2008-Jan-20, 06:29 AM
We would need orders of magnitude better noise rejection. So that answer your question Antoniseb; no, I personally doubt gravity probe B v2.0 would be sufficient to satisify everyone.

Jerry
2008-Jan-21, 05:02 AM
Do you think that enough information was collected to enable doing it better next time?

I think a Cavendish-type experiment inside or outside the orbit of the earth would be the best definitive test. In fact we need a 'primary science' mission verifying instrument performance with as many primary standards as is practical.

antoniseb
2008-Jan-22, 12:52 PM
I think a Cavendish-type experiment inside or outside the orbit of the earth would be the best definitive test. In fact we need a 'primary science' mission verifying instrument performance with as many primary standards as is practical.
Can you explain how that might measure this effect more precisely. I'm not saying it can't, just that I don't know the limits of measurement, or completely understand what you're proposing to measure here. It might be a pretty interesting experiment.

nutant gene 71
2008-Jan-22, 05:07 PM
I think a Cavendish-type experiment inside or outside the orbit of the earth would be the best definitive test. In fact we need a 'primary science' mission verifying instrument performance with as many primary standards as is practical.
One way is to measure for 'inertial mass' per Equivalence Principle. If the inertial mass proves different at different orbits around the Sun, say at Mercury for one test, and Mars for another test, to see how much force F=ma is needed to accelerate a given mass, then per equivalence, we might have a reading for Newton's G. Not exactly a Cavendish-type, but might have same indirect 'gravity' effect, something GP-B could not test for in Earth's orbit.

BTW, test around Earth's orbit doesn't count. It has to be away from 1 AU.

lpetrich
2008-Jan-23, 09:34 PM
The Confrontation between General Relativity and Experiment (http://relativity.livingreviews.org/Articles/lrr-2006-3/), by Clifford M. Will, is a comprehensive discussion of experimental tests of GR and alternative gravity theories.

In section 3, he discusses "Tests of Post-Newtonian Gravity", in which he confines himself to "metric" theories of gravity, where gravitational effects are communicated to matter by way of the space-time distance function or metric.

Making some reasonable assumptions about the possible forms of the metric coefficients yields a metric with ten parameters. They are:

gamma: amount of space curvature
beta: a superposition amount
xi: preferred-location effect
alpha1, alpha2, alpha3: preferred-frame effects
alpha3, zeta1, zeta2, zeta3, zeta4: violation of momentum conservation

Linear-momentum conservation: alpha3 = zeta1 = zeta2 = zeta3 = zeta4 = 0
No preferred frame (angular-momentum conservation): alpha1 = alpha2 = alpha3 = 0

GR: gamma = beta = 1, all others = 0


The parameter gamma can be measured by finding the deflection and time delay of light and radio signals. The PPN values of these quantities is
(1 + gamma)/2 * (GR value)

Soldner's Newtonian calculation is equivalent to gamma = 0.

The most precise measurement of it so far, from the Cassini spacecraft, yields
gamma - 1 = (2.2 +/- 2.3)*10-5


Post-Newtonian effects will cause orbits to precess by an amount
(2 + 2*gamma - beta)/3 * (GR value)

From the extra percession of Mercury's orbit,
|beta - 1| < 3*10-3


Turning to the effects that Gravity Probe B had measured,

Geodetic effect = (2*gamma + 1)/3 * (GR value)
Gravitomagnetic effect = (1 + gamma + alpha1/4)/2 * (GR value)
a.k.a. frame dragging and Lense-Thirring effect


So any theory of gravity that reduces to PPN form in the appropriate limit will have its value of gamma constrained by the Gravity Probe B results.

From the results quoted by hhEb09'1,

Geodetic precession = 6632 +/- 43 (GR = -6571)
GR-relative - 1 = (0.93 +/- 0.65) * 10-2
gamma - 1 = (1.39 +/- 0.98) * 10-3

Frame-dragging = -82 +/- 13 (GR = -75)
GR-relative - 1 = (0.09 +/- 0.17)
gamma - 1 = (0.19 +/- 0.35)
(assuming alpha1 = 0)


BTW, I wonder how well the theories in Nereid's reference fit into the PPN formalism; I know that that's the case for some of them, like GR itself and the Generalized Brans-Dicke theory.

Jerry
2008-Jan-24, 05:26 AM
Can you explain how that might measure this effect more precisely. I'm not saying it can't, just that I don't know the limits of measurement, or completely understand what you're proposing to measure here. It might be a pretty interesting experiment.
Two spherical probes linked to each other by a single thread in a highly elliptical orbit about the sun. The weak gravitational force between them would result in a minute tension on the thread, measurable with differential strain gages. If Newtonian concepts are wrong, the variation in the tension between the spheres will be a function of solar distance. It would take several orbits to sort out the degeneracies caused by the solar wind and such, but it would be simple and straight forward.

And there are other simple tests: vibrating a known mass at a known frequency: How much energy does it take? Cassini scientists are having a difficult time with the small motors used to control gratings and such, is this a clue? There have been numberous problems with electromechanical devices, especially reaction wheels and gyroscopes; and this is one place I have looked for, but not found a common thread. Information published on fuzzy systems is often sketchy. I don't know - does it take more or less energy than expected to spin-up Cassini's reaction wheels?

antoniseb
2008-Jan-24, 02:06 PM
Two spherical probes linked to each other by a single thread in a highly elliptical orbit about the sun. The weak gravitational force between them would result in a minute tension on the thread, measurable with differential strain gages. If Newtonian concepts are wrong, the variation in the tension between the spheres will be a function of solar distance.

These are some interesting ideas. Can you diagram or describe in more detail what you mean by this first one? I'm imagining that there would be some issues with the tension on the string. How are you thinking the two spheres should be oriented with respect to the path of the orbit?

trinitree88
2008-Jan-27, 07:32 PM
Can you explain how that might measure this effect more precisely. I'm not saying it can't, just that I don't know the limits of measurement, or completely understand what you're proposing to measure here. It might be a pretty interesting experiment.

Antoniseb. Actually it's essentially a test for the constancy of Big "G". The Bureau of Standards and all scientists being confined to our environs....sensitive experiments to determine G have been done classically with Eotvos-type apparatus. In more recent decades, Mossbauer effect tests for small variations in local g fields have evolved with sensitivity being inversely proportional to bandwith, and bandwidth approaching monochromaticity...hence a graser. As this stuff is very sensitive and highly classified, you're going to need a "Q" level clearance to talk about it sensibly with the people in charge. It's why I proposed the Mossbauer test near a refueling nuke plant in 1982. A minute acceleration will produce a resonance detuning of the apparatus, but so will a gravitational gradient. Both of those are accompanied by a commensurate shift in the neutrino sea gradient which is omnipresent. Jerry's thinking of a Cavendish-type apparatus is OK and could carry out the result if launched in a satellite that journey's out to Pluto and back....but due to the torsion balance nuances, with great sensitivity to mechanical vibrations, a Mossbauer test is far more robust. Solid State. Zirconium steel tubes. No delicate springs to withstand a shuttle or rocket launch. The solar neutrino flux is likely anisotropic due to parity effects, and zodiacal gas and dust in the solar plane should cause a varying value of "G" depending on R, theta, and phi....and a bit of MOND. Had this discussion with Ken G in a few e-mails two years ago. Didn't open it up in the forum, or in my physics talks at the AAPT because it was predicting flat rotation curves at large R, which Vera Rubin discussed at MIT years ago, and I had no data to work on, or access to be a principal scientist in an investigation...so I routinely left it out.
The other thing that should show up is a persistent change of solid state "shot noise" vs R, theta, and phi from the sun. The guillotine once again, a first rate theory predicts...I'll bet a bottle of Rob's Root Beer. pete.

antoniseb
2008-Jan-27, 08:09 PM
...Both of those are accompanied by a commensurate shift in the neutrino sea gradient which is omnipresent. Jerry's thinking of a Cavendish-type apparatus is OK and could carry out the result if launched in a satellite that journey's out to Pluto and back....but due to the torsion balance nuances, with great sensitivity to mechanical vibrations, a Mossbauer test is far more robust...

While I have no reason to believe that the density of neutrinos has any impact on 'G', let's assume that it is something you'd like to test. There was a proposed mission to launch a pair of dense spheres which would be loosely contained in a sphere of nearly uniform density including an ion engine to keep the outer sphere moving in an ideal ballistic path (measured by the motion of the inner spheres). This keeps dust, solar wind, and other factors from affecting the experiment. The experiment will test how the two inner spheres orbit each other.

Given your idea, there's no reason other than price that such an experiment couldn't be put on a New Horizons type trajectory. Would this give the kind of precision you are looking for?

Jerry
2008-Apr-28, 08:06 PM
GP-B Program Extended Through September 2008, and Possibly March 2010


On November 2, 2007, we convened the 17th meeting of our external Science Advisory Committee (SAC) to review our progress in the refinement of the GP-B experimental results. The subsequent SAC report noted "the truly extraordinary progress that had been made in data analysis since SAC-16 [March 23-24, 2007]" and unanimously concluded "that GP-B is on an accelerating path toward reaching good science results."

Following a peer-reviewed bridging proposal to NASA's Science Mission Directorate (SMD) and actions by Stanford and a private donor, the GP-B program has been extended at least through September 2008.


http://einstein.stanford.edu/highlights/status1.html

...and possibly through 2010? Without releasing any concrete information as to whether the current data set is consistent with General Relativity or not? This program is already more than forty years old - we could all die before anything concrete is published!

Gsquare
2008-May-06, 05:15 AM
One expects the polhode moment of an egg to vary over eighteen months, but not a set of spheres made from materials chosen because of their known (presumed?) stability. It would seem to be a worthwhile test of the varacity of this 300,000,000+dollar assumption to construct a duplicate set of spheres and see if the polhode properties on earth are the same as they are in the heavens.

I can understand your logic, Jerry, but...
doing that would obviate the whole reason for using a zero g environment in the first place....at least for gyroscopes.

Do you think the exact polhode precession could be duplicated precisely.?
Even if the spheres could be duplicated exactly, duplicating the space environment on earth would not be possible, neither would it be possible to duplicate the precise patch effect....and its response in a zero g environ.

Most are unaware that the original conception was to do earth-based gyros, but it was easily shown that the suspension and unbalanced mass torques on earth-based gyros were far more problematic than that of their (greatly improved) performance in zero g.

Furthermore, working out the equations for constrained motion for gyroscopes (earth-based) is far more complex, and even though they were eventually obtained for the geodetic precession (only ~0.4 arcsec/yr. on earth), I am not sure the frame dragging portion of the precession was ever obtained precisely for constrained gyro motion, especially since there were some ambiguous assumptions in doing so.

So 'modeling' the polhode from the orbital data is appropriate.

. Here's a video simulation of the modeled Polhode effect over time....from the orbital data:
http://einstein.stanford.edu/Media/Polhode_motion-animation.html

Now, having said all that...I want you to realize there actually was pre-launch testing of possible Polhode effects; its just that, in part, because of the above mentioned complications in constrained moton, that modeling did not match the orbital data....at least that's the assumption.

Do I think the polhode theory provides the definitive answer for the anomalous precession? Not necessarily; and I think that other 'causes' should be suspected and modeled....especially since the introduction of Tajmar/ deMatos's unusual experimetal results ...which indicate much larger Gravitomagnetic response of superconductors than would otherwise be expected by GR. (More on that in the bold print below).

G^2



OK, that is a legitimate premise: If a torsion gravity theory is correct, One would expect this hypothetical angular momentum coupling to be time variable; that is, to effect the rotational moments of the Gravity B probe.

We know the rotational moments of the Gravity B probes did change over time, and this unexpected change is thought to be due to electrostatic coupling and a time-dependent Polhode moment. If this unexpected momentum is due to torsion coupling;.....


Excellent ; Jerry; you are thinking outside the box now....the GR box. :D

We should follow GR as far as it can take us; but it is important to realize it does have its limits and when we get to its limitations, it is appropriate to take the next step by considering possibilities beyond its scope.

I believe it was Hehl who admitted that Gen Rel. was not at all adept in handling correlated spins. If I remember his comment was along the lines that GR has an axiom that all motion can be transformed away by an appropriate choice of reference frame, but with correlated spins that is not possible. Thus he, like others, have recognized the limitations of GR.
Your recognition of that point is noted.

........

**The other modeling I would like to see (in GP-B) is that which would take into account the Tajmar / deMatos effect. As I mentioned to Publius some time back, the greatly enhanced gravitomagnetic field of the gyros should not influence the frame dragging precession portion of the experiment.....BUT that was ONLY considering its interaction (or lack of interaction) of a SINGLE gyroscope with the earth's gravitomagnetic field.

The problem developes when we realize there are FOUR gyros in GB-P, two spinning one direction and 2 spinning the other direction....(which was done for redundancy to cross check and make for greater accuracy in the data).

If we consider the multiple effects of 4 greatly increased GM fields of the 4 SC gyroscopes, then we have to deal with their INTERACTION WITH EACH OTHER. Surely if the gravitomagnetic field of a superconducting Gyro is enhanced as great as Tajmar experiments suggest, then the interaction of the dipole GM field of each gyro with the others must be taken into account.

Even though each gyro is magnetically isolated, it is impossible to gravitomagnetically isolate them....Gravitomagnetism is an angular momentum transferring field, the interaction between gyros of which can very possibly mimic unbalanced torque (or at least confound any modeling) of polhode / electrostatic coupling of the gyro to the frame.

Hope that all made sense.
All comments welcome.:D
.
G^2

alainprice
2008-May-07, 04:38 PM
When can I pop the bubbly?

2010? *sigh*

trinitree88
2008-May-07, 06:04 PM
SNIPPET. G 2.Understood SNIPPET

Even though each gyro is magnetically isolated, it is impossible to gravitomagnetically isolate them....Gravitomagnetism is an angular momentum transferring field, the interaction between gyros of which can very possibly mimic unbalanced torque (or at least confound any modeling) of polhode / electrostatic coupling of the gyro to the frame.

Hope that all made sense.
All comments welcome.:D

.
G^2
SNIPPET That's not the only thing it's impossible to isolate from either. pete

Jerry
2008-May-08, 02:36 AM
Hope that all made sense.
All comments welcome.:D
.
G^2
Yes, very good, thank you.

In a later release, the Gprobe website stated all of the variance could possibly be accounted for in patch effects; rather than a combination. If you followed the experiment from the start, you know they placed much emphasis on the fact that all of the data reduction techniques were in place before the probe was launched, including the anticipated corrections necessary due to in-flight calibration checks.

In trying to back-out the data due to unanticipated results, there must be assumptions. Splines on top of splines - Every additional month of data massaging reduces the credibility of the product.

Gsquare
2008-May-11, 06:57 AM
That's not the only thing it's impossible to isolate from either. pete

True, Pete. Don't know what you're getting at, but there are several other relativistic effects that are known to alter the precesssion of the gyroscopes which must be subtracted from the data.

1.There is a correction to the geodetic precession due to earth's oblateness....which amounts to about 7 milliarc sec/yr.

2. There is a SOLAR geodetic precession sometimes called the DeSitter-Fokker effect which is identical to the terrestrial geodetic effect, but is due to the mass of the sun.....and which amounts to....(let me check....you don't think I remember all these figures do you? :D).....OK, about 19 milliarc sec/yr.

3. And there is starlight deflection from the guide star (due to the solar gravitational field) which varies through the year due to guidestar's changing position with respect to the sun as viewed from earth. I'm not sure of its value but probably varies between 0 and 15 or 20 milliarc sec. or so during the year.

None of these can be 'shielded' against....and they are simply calculated and subtracted from the data stream.

These above are the only three relativistic effects (besides the ones GP-B is designed to measure - earth's geodetic and frame dragging) that I know about which have been accounted for .

The other effect which I know has not been included is the spin-spin gravitomagnetic interaction between the gyroscopes that I have been pointing out in my previous post.

G^2

BTW,
(There are other completely distinguishable non-relativistic signals superimposed on the above,.... some variable...like aberration of starlight, etc. that also must be accounted for;.. but I only wanted to mention the relativistic ones).

-----------------
--"What's another name for thessaurus?" -- :D

ToSeek
2008-May-20, 09:43 PM
Gravity Probe B scores 'F' in NASA review (http://space.newscientist.com/article/dn13938-gravity-probe-b-scores-f-in-nasa-review.html?DCMP=ILC-hmts&nsref=news3_head_dn13938)


A NASA review appears to spell the end for Gravity Probe B, the project conceived in the 1960s to measure how the Earth warps the fabric of nearby space-time.

A panel of about 15 experts commissioned by NASA analysed the performance of 10 NASA astrophysics missions that are currently operating in Earth orbit. A copy of the "senior review" obtained by New Scientist concludes that extending the lifetimes of the top nine missions "would be certain to deliver unique data of high scientific value". But Gravity Probe B didn't make the cut because the panel doubted further analysis of its results would yield significant new information.

Building and launching spacecraft is expensive, so maximising the use of those already in orbit can offer big benefits. But the expert panel said NASA didn't have the budget to support all the worthwhile missions.

It recommended that Gravity Probe B receive no additional funding after its current funding runs out in September.

ToSeek
2008-May-20, 10:02 PM
Ten (!) threads about Gravity Probe B merged, including five entitled "Gravity Probe B".

CJSF
2008-May-20, 11:24 PM
2 things:

ToSeek: Does merging 10 threads make things problematic, in terms of following conversations?

Generally: So, does this mean that Gravity Prob B = teh suck or just that there is no need to keep it operating? Was it considered a success, or is that TBD?

CJSF

ToSeek
2008-May-21, 01:28 AM
ToSeek: Does merging 10 threads make things problematic, in terms of following conversations?


You tell me. Most of the threads seemed to be temporally independent, so I don't think merging them should be much of a problem.

EDIT: I just went through the thread, and I think the only confusing things are the references to other threads that are no longer separate threads, but some of those didn't work even before I did the big merge.

CJSF
2008-May-21, 12:09 PM
You tell me. Most of the threads seemed to be temporally independent, so I don't think merging them should be much of a problem.

EDIT: I just went through the thread, and I think the only confusing things are the references to other threads that are no longer separate threads, but some of those didn't work even before I did the big merge.

Fair enough. In this case merging the 10 seems to be a good idea.

CJSF

ToSeek
2008-May-21, 02:06 PM
Fair enough. In this case merging the 10 seems to be a good idea.

CJSF

Well, I have to admit that part of the appeal is having the 245th thread on this forum still be an active one. ;)

Jerry
2008-May-27, 01:45 PM
Gravity Probe B scores 'F' in NASA review (http://space.newscientist.com/article/dn13938-gravity-probe-b-scores-f-in-nasa-review.html?DCMP=ILC-hmts&nsref=news3_head_dn13938)

...we were greatly surprised last week to discover that the Sr. Review had recommended that NASA not grant our final funding extension, particularly since another NASA committee--the GP-B Science Advisory Committee (SAC -- http://einstein.stanford.edu/MISSION/mission2.html#sac), chaired by relativistic physicist Clifford Will--stated in its report following the November 2007 meeting: "The SAC was impressed with the truly extraordinary progress that has been made in data analysis since SAC-16 [Mar 2007] Š and we now agree that GP-B is on an accelerating path toward reaching good science results."

The Sr. Review evaluation is an unexpected setback, but we are determined to push ahead and drive to the very best possible result within the resources available.
Funding runs out in September.

I have mixed feelings about this. I hate to see any science team disassembled; and I believe gravity is not understood at the most fundamental level - we need this type of science team, and more experiments of this type.

What is disappointing, is that they have not really released anything useful years after the end of the mission.

As far as the data, either there is an unexpected 'patch effect' that the team has focused their attention on, or the physics behind their observations is not understood, or both. I said several pages up I would rather see another mission, or a construction of new spheres to see if the type of patch effects they speculated entangled their data are the root cause of the failure to observe frame dragging effects.

In any case, I hope the final report includes some salvagable data, and clues for where we should keep looking.


Now, in 2008, the scientific justification for completing the GP-B experiment is even more valid. During the past five years, there has been little progress on other relativity experiments, but GP-B was launched, operated, and collected all of the necessary data. After two years of intense work, the GP-B science team is very close to completing the data analysis.
Perhaps it is time to look elsewhere.

Sam5
2008-May-28, 03:56 AM
In any case, I hope the final report includes some salvagable data, and clues for where we should keep looking.



There is something called a Final Report here:

http://einstein.stanford.edu/

See right side page and click on Final Report. It's a 12 meg pdf file.

http://einstein.stanford.edu/content/final_report/GPB_FinalPFAR-091907-scrn.pdf

So what's the result of all this testing so far?

ngc3314
2008-May-29, 12:42 AM
Generally: So, does this mean that Gravity Prob B = teh suck or just that there is no need to keep it operating? Was it considered a success, or is that TBD?


The biennial senior reviews are generally tasked to rank extended (post-primary-mission) support for a number of missions (and sometimes archive services) under the purview of NASA astrophysics, with regard to the likely science impact specifically of the proposed extended funding period. This year, they had to rank Swift, Chandra, GALEX, the warm extension for Spitzer, NASA funding for US investigators with XMM-Newton and INTEGRAL, operation of RXTE, two additional years of operation for WMAP, and extended analysis funds for GP-B (which ceased actual operations some time back). As I read the snippets of the review that have shown up around the web, the feeling (which I would have shared) was that it appeared unlikely that they could get a result from the additional 2 years or so which would be definitive (i.e. believed by anyone not on the team, to put things crudely). The decisions are often painful, but I agree that they are more fruitfully made by scientists than on other grounds.

CJSF
2008-May-29, 02:30 AM
O..K... so, they haven't gotten anything useful and are unlikely to with the additional two years then....

?

I just haven't, to my recollection, read about a failed mission before this. I mean, scientists and engineers have always managed to pull SOMETHING out of things...

CJSF

Sam5
2008-May-29, 04:16 AM
O..K... so, they haven't gotten anything useful and are unlikely to with the additional two years then....

?

I just haven't, to my recollection, read about a failed mission before this. I mean, scientists and engineers have always managed to pull SOMETHING out of things...

CJSF


http://www.misunderstooduniverse.com/Gravity_Probe_B_Cosmic_Money_Pit.htm